Limit stop for parallelogram mechanisms



Nov. 21, 1950 J. R. PICON LIMIT STOP FOR PARALLELOGRAM MECHANISMS Filed July 21, 1947 3nnentor Patented Nov. 21, 1950 LIMIT STOP FOR PARALLELOGRAM MECHANISMS Josue R. Picon, Detroit, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application July 21, 1947, Serial No. 762,237

Claims.

The present invention relates to limit stopsfor parallelogram mechanisms. More particularly it relates to a floating limit stop for universal head drafting machines using four bar double parallel crank mechanisms.

To permit the greatest possible utilization of the advantages of universal head drafting machines, it is necessary that the head have freedom of movement to any part of the drafting board. Unless precautions are taken to limit the movement of the head in the horizontal axis it is possible to inadvertently move the drafting head to such a position that it clears the edge of the drafting board and falls vertically with resulting damage to the mechanism.

Previous to the present invention the draftsmen using universal drafting machnes had difiiculty in using such a machine with great flexibility, and at the same time avoid damage due to inadvertent movement of the universal head over the edge of the drafting board.

It is therefore an object of the present invention to produce a limit stop for parallel bar crank mechanisms that is economical to manufacture and foolproof in operation.

It is a second object of the present invention to produce a limit stop for universal head drafting machines which limits the horizontal travel of the drafting head.

Other objects of my invention will become obvious upon reading the specification and inspection of the figures of the drawing.

Referring to the figures of the drawing:

Figure 1 is a plan view of a universal head drafting machine incorporating the present invention.

Figure 2 is a sectional view through line 2--2 of Figure 1.

Figure 3 is a partial sectional plan view taken through the line 3-3 of Figure 2.

Referring more particularly to the figures of the drawing, in Figure l, 2 is a drafting table or board having a drafting surface 4 and a machine supporting surface 6. The drafting machine is attached to the surface 6 by means of projection 8. This universal head drafting machine is of the conventional type having upper pivot mechanism I0 and lower pivot mechanism I2. These two pivot mechanisms are connected by means of parallel bars I4 and It. The bar I4 is pivoted to the mechanism ID at the point I8 and to the mechanism I2 at the point 20. The bar It is pivoted at the points 22 and 24. The distance between points I8 and 20 is equal to the distance between the points 20 and 24. The bar I4 from point I8 to point 26 is exactly the same length as the bar I6 from point 22 to point 24.

Located on the mechanism I2 at points to the points 20 and 24 are pivot points26 and 28. Two parallel bars 36 and 32 are pivoted respectively at the points 26 and 28. The opposite ends of these bars are pivoted to the universal drafting head 34 at points 36 and 38. As explained in connection with the bars I4 and I6, the bars 36 and 32 also form two sides of a parallelogram.

Referring to Figures 2 and 3, the means of incorporating the present invention in a conventional drafting machine is shown in some detail. As shown in these two figures, the drafting machine has freedom of vertical movement around the pin 40. With the exception of the limit stop 42 the mechanism It shown in these two figures is of conventional construction. This construction incorporates an upper plate 44, and a lower plate 46 which carry the pivot pins I8 and 22. Located midway between these pivot pins is the pin 48 which is utilized in the present invention to support the limit stop 42. The limit stop 42 consists of a washer having an internal diameter considerably greater than the diameter of the pin 48. The external diameter of this washer is considerably less than the distance between the points I8 and 22. As shown in Figure 2, this washer is assembled in the assembly In between the plates 44 and 46 and mounted in a fixed axial position with limited freedom of radial movement.

The operation of this limit stop is as follows:

The arms I4 and I6 pivot about the points I8 and 22 as the drafting head 34 is moved in a horizontal direction. As the drafting head is moved to the left the arm It moves clockwise around the point 22 until it engages the limit stop 42 and the internal surface of that limit stop engages the pin 48. At that point the horizontal movement to the left of the universal head is arrested before the universal head has cleared the surface of the drafting board 4.

As the universal head is moved to the right, the arm I4 moves about the pivot I8 in a counterclockwise direction. This movement is continued until the arm I4 engages the washer 42 and movement is arrested by this washer engaging the pin 48.

It may thus be seen that by the use of the present invention the vertical movement of the drafting head is unrestricted while its horizontal movement is restricted to the surface of the drafting board 4.

It is to be understood also that although the invention has been described with specific reference to a particular embodiment thereof, it is not to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.

I claim:

1. In parallelogram crank mechanisms with two parallel long arms and two parallel short arms each pair of adjacent ends of said long arms being connected to the opposite ends of each of said short arms respectively, one of said short arms being fixed to a laterally stationary supporting member and the other short arm being laterally movable relative thereto, including a pin located midway between the ends of one of the short arms, a floating limit stop including a washer surrounding said pin, said washer having an internal diameter greater than the diameter of said pin and an external diameter less than the distance between said long arms so located that the washer is simultaneously engaged by one of said long arms and said pin to provide a limit stop for said mechanism.

2. A drafting machine as claimed in claim 1 in which the floating limit stop washer has an internal diameter of at least twice the diameter of the pin it surrounds.

3. A drafting machine as claimed in claim 1 in which the difference between the external diameter and the internal diameter of the floating limit stop washer is less than one-half the dimension of the short arm.

4. A drafting machine as claimed in claim 1 in which the pin is located midway between the ends of the short arm fixed against lateral movement.

5. In a parallelogram crank mechanism with two parallel long arms and two parallel short arms each pair of adjacent ends of said long arms being connected to the opposite ends of each of said short arms respectively one of said short arms being fixed to a laterally stationary supporting member and the other short arm movable relative thereto, including a pin located midway between the ends of the laterally fixed short arm, a floating limit stop including a washer having an internal diameter of at least twice the diameter of the pin it surrounds, the difference between the external diameter and the internal diameter of said washer being less than one-half the dimension of the short arm such that the Washer is simultaneously engaged by one of said long arms and said pin to provide a limit stop for said mechanism.

J OSUE R. PICON.

REFERENCES CITED UNITED STATES PATENTS Name Date Little May 16, 1933 Number 

